May/June 2015 | Volume 34 No3.
By Frank Steegmanns, STOCKMEIER Urethanes GmbH & Co.KG and Melissa Martinkat, STOCKMEIER Urethanes USA, Inc.
It is well known that filters are an important product for the world. They are used to protect health, the environment, and to extend the longevity and efficiency of products. Filter manufacturers understand that a filter is only as effective as its components, including adhesives, sealants, and casting systems. Polyurethane and epoxy systems for filters in automotive and industrial applications have been a leading technology for many years. This means that users can rely on a wide range of approved materials. The increasing demands on filters and filter applications, particularly in the automotive arena, means the adhesive, sealants, and casting systems are continuously being adapted to the latest standards. Various systems have been developed to meet different applications, which then become established as the manufacturing standard. The primary focus at STOCKMEIER Urethanes is developing and manufacturing polyurethane systems.
STOCKMEIER Urethanes, a specialist within the STOCKMEIER Group, is an ISO 9001 certified polyurethane systems manufacturer that specializes in the production and development of coatings, adhesives, sealants, and elastomers. Included among the polyurethane systems product lines is Stobicoll┬« F. This line encompasses polyurethane adhesives, sealants, and elastomers suitable for oil, hydraulic, fuel, dust, powder, HVAC, HEPA/ULPA, gas turbine, pleat, and automotive air filters. Founded in Germany in 1991, the company has laboratories and manufacturing facilities in Germany, France, the United States, and the United Kingdom.
Polyurethane – The Classic System for Filters
Polyurethane systems for filter applications are generally used as a two-component system. The systems can be filled or unfilled according to the application. The viscosity of polyurethanes varies between a thin liquid with excellent flowing properties to a paste or thixotropic performance for pre-assembling. The hardness of typical filter adhesives, measured in shore hardness, ranges from very soft with a shore hardness of approximately 5A to very rigid with a shore hardness of approximately 95D. The long-term temperature can be from approximately 120┬░C (248┬░F) up to a maximum of 140┬░C (284┬░F) for some special formulations. Additionally, polyurethane can be formulated as a slightly foamed or full foamed product. Filled and rigid polyurethanes can be formulated to resist glycols, biodiesel, or synthetic oils, making them ideal for automotive applications. For industrial uses such as the food industry, certified according to FDA and EC 1935:2004, or clean room applications, certified according to VDI 6022, a variety of polyurethane systems are available with a wide range of color options. Together with the flexible pour and curing times, polyurethane is suitable for just about any production process and therefore the most diverse system for filtration.
Applications of Polyurethane Systems
One of the most common applications in the automotive and automotive aftermarket industries is in the production of various panel air filters. To keep the filter production as cheap and effective as possible, the filter cell is placed into a mold and a polyurethane foam adhesive is injected. This polyurethane foam stabilizes the filter cell and forms a soft seal onto the filter housing. Polyurethane systems are also used to bond parts inside an oil-filter cartridge. A lightly foamed polyurethane system is often used for cost reasons. In industrial applications, various polyurethane systems are used as end cap sealants to stabilize the filter pleat and simultaneously seal onto the filter housing. The shore hardness of polyurethane systems can be adjusted according to application.
Additionally, the filter pleat is placed into a mold and filled with a fluid polyurethane casting material. Further industrial applications for polyurethane systems can be found in a variety of air and dust filters. The frames on these filters are made from various substrates. This includes plastics, such as ABS or polystyrene, aluminum, or derived timber products. In these applications, the complete filter is pre-assembled and later filled with liquid polyurethane adhesives. A thixotropic version of polyurethane can also be used in this application. In this case, the material is poured into the frame before assembling the filter. The thixotropic material ensures the adhesive stays within the frame while the product adheres to the filter pleat.
Outlook and Completed Developments
High volume production of items such as automotive oil filters and fuel filters is slowly bringing commonly used application systems to their capacity limits when using static or dynamic mixing. Faster application of the glue, especially in small quantities, is only possible using high-pressure application machines. These machines are yet to be developed to handle filled polyurethane systems, which are typical when combating mediums such as glycol, biodiesel or oils. Developing an unfilled system that is resistant to these materials so they can be applied, using a high-pressure machine, is therefore required, and currently this research is now at an advanced stage. Also under development are adhesives that by curing at room temperature have the ability to absorb oil and process additives from the substrate’s surface. This could eliminate the need to pretreat the metal end caps. Additionally, research is underway to replace the metal end caps with specially formulated adhesive systems and polyurethane systems for high temperature applications up to 160┬░C (320┬░F). Lastly, development of antistatic conductive adhesives have been completed, namely Stobicoll F 483 and F 484. These adhesives are used in the production of ATEX filters and helps control the voltage while simultaneously sealing and stabilizing the filter. All of these developments would result in filter manufacturers seeing a reduction of both process time and production costs.
For more information contact:
Frank Steegmanns, Key Account Manager Adhesives
STOCKMEIER Urethanes GmbH & Co.KG, Lemgo, Germany
Tel: +49 (0) 52 61 / 66 0 68 – 0
Julia Prendergast, Business Director of Cast Elastomers, Filtration and E&E
STOCKMEIER Urethanes USA, Inc.
Tel: +1 304 624 7002